1. Field of the Invention
The present invention relates to an accumulator for an airless spraying apparatus, and in particular to an accumulator for a compact, transportable or portable airless spraying system which is capable of producing superior results with ultra low volumes of paint or other liquid to be sprayed.
2. Description of the Prior Art
It has been proposed before to use an accumulator as part of an airless spraying system. The accumulator includes a pressure vessel with a slideable piston in the vessel. On one side of the piston is an expansible chamber which receives the paint or other liquid to be sprayed under pressure. The piston moves to the rear of the accumulator and the chamber expands as it is charged with pressurized paint or other liquid. On the other side of the piston is an energy storing section which may take the form of nitrogen gas under pressure. The energy storing section containing the nitrogen gas contracts as the piston moves to the rear of the accumulator, further compressing the nitrogen gas and thus storing energy for effecting a smooth and complete discharge of liquid under high pressure during spraying.
One difficulty with the use of such an accumulator is providing adequate lubrication for the sliding piston. It is important in this regard to avoid any substantial presence of lubricant in the expansible chamber containing the liquid to be sprayed, since this can contaminate the liquid. It has been known to provide accumulators in which lubricant is contained in the chamber representing the energy storing section. The piston is open to communicate with the energy storing section to effect lubrication of the seals on the piston. This, however, is not entirely satisfactory because it requires a large amount of lubricant and results in considerable dilution of the lubricant when it is spread throughout the entire energy storing section. These undesirable conditions are aggravated when the piston is moved entirely to the front of the accumulator to completely discharge the expansible chamber containing the liquid to be sprayed. In this circumstance, the chamber representing the energy storing section becomes almost the entirety of the pressure vessel. Such an arrangement runs counter to the goal of a self-contained lubricant adequate for long-term use.